Bacteremic infection is a major cause of morbidity and mortality in infants and children. Although antibacterial agents are highly effective in treating these infections, it remains difficult to accurately diagnose these patients. This study will measure cytokines known to either directly or indirectly mediate cellular responses characteristic of bacteremic infection caused by encapsulated bacteria in children and infants with febrile illnesses. It is expected that this will improve our knowledge of the immunology of these infections.